1. Field of the Invention
This invention relates to automatic/semiautomatic power transmissions providing a plurality of gear reduction ratios, such as automatic/semi-automatic mechanical transmissions (i.e. "AMTs"), and, to control systems and methods therefor. In particular, the present invention relates to control systems and methods for automatic/semi-automatic mechanical transmission systems wherein gear selection and shift decisions are made and/or executed based upon measured and/or calculated parameters such as vehicle or transmission output shaft speed, transmission input shaft speed, engine speed, throttle position, rate of change of throttle position, rate of change of vehicle and/or engine speed and the like. More particularly, the present invention relates to a control and method for controlling an AMT system including detection of in-gear faults (i.e. transmission not engaged or engaged in a ratio other than the ratio indicated by control logic) and tolerance thereto.
2. Description of the Prior Art
The use of automatic transmissions of both the automatic mechanical type utilizing positive clutches and of the planetary gear type utilizing frictional clutches is well known in the prior art as are control systems therefor. Electronic control systems utilizing discrete logic circuits and/or software controlled microprocessors for automatic transmissions wherein gear selection and shift decisions are made based upon certain measured and/or calculated parameters such as vehicle speed (or transmission output shaft speed), transmission input shaft speed, engine speed, rate of change of vehicle speed, rate of change of engine speed, throttle position, rate of change of throttle position, full depression of the throttle (i.e. "kickdown"), actuation of the braking mechanism, currently engaged gear ratio, and the like, are known in the prior art. Examples of such automatic/semi-automatic transmission control systems for vehicles may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 4,576,065; 4,648,290; 4,569,255; 4,551,802; 4,527,447; 4,425,620; 4,463,427; 4,081,065; 4,073,203; 4,253,348; 4,038,889; 4,226,295; 3,776,048, 4,208,929; 4,039,061; 3,974,720; 3,478,851 and 3,942,393, the disclosures of which are all hereby incorporated by reference.
Automatic control systems/subsystems for automatically controlling the engagement and disengagement of AMT system vehicle master clutches, especially during vehicle start from stop operations, are known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,081,065; 4,401,200; 4,413,714; 4,432,445, 4,509,625 and 4,576,263, the disclosures of all of which are hereby incorporated by reference.
While the above referenced automatic/semiautomatic transmission control systems, especially the systems illustrated in U.S. Pat. Nos. 4,081,065; 4,361,060; 4,595,986; 4,576,065; 4,569,255 4,648,290; and 4,576,263, and similar systems, are effective to control the vehicle automatic/semiautomatic transmission system operations under most conditions, under certain conditions, the logic did not accurately sense an unintended out of gear or incorrect gear engaged condition and/or did not provide adequate response to such conditions.
In particular, upon commanding engagement of a particular selected gear ratio in an automatic/semi-automatic multiple speed mechanical transmission, verification of actual engagement is often a matter of sensing actuation of a particular solenoid or set of solenoids, sensing axial movement of a particular shift rail, shift piston or shift fork, or the like.
Due to the possibility of faulty position sensors, excessive deformation or clearance in, or failure of, a portion of the shift linkages, and the like, it was not possible to sense with the desired degree of certainty when a selected gear ratio did not achieve initial engagement or, due to drive line conditions, "fell out of gear". Not being engaged in the selected gear ratio, or at least one of the gear ratios, can be a very undesirable condition, especially in a heavy duty truck traveling down hill.